Ground Roof on FPSF
Hello,
I am working out the details on my fpsf, zone 6 coastal maine. I have 4 feet of wing insulation all the way around and I am using type II EPS. There will be a 4 inch footing drain exterior of the grade beams as well. The wing insulation will be pitched out slightly to shed water and it will essentially rest on the 4 inch pipe at the grade beam. Is it necessary to top the EPS with EPDM to promote water drainage? There will be 1 foot of soil over the EPS and i have 2 foot overhangs. Also, should I seal the connection between the vertical EPS on the exterior face of the grade beam and the wing insulation with wigluv? Hoping to avoid fentrim due to cost.
Thanks,
Stephen
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
It depends... the building code requires foam frost wings to be protected by something rigid if less than 12" below grade, not that anyone enforces that particular rule. If you install a layer of clay or clay-loam mix at grade, that will block a lot of stormwater from reaching the foam, vs. installing a drip course of 3-4" crushed stone will direct stormwater downward. If your site is on a slope with well-drained soil, and you have solid PVC footing drains to open air, that is a much more forgiving situation than being on a low, wet site or on clay. Large roof overhangs will direct a lot of water away from the house--unless you live in a place where the wind blows when it's raining, such as coastal Maine--vs. a "monopoly house" with no overhangs. If you have gutters (and no trees near the house, and/or really effective gutter covers, if there is such a thing) and the downspouts lead to a drainage system, that's more forgiving than relying on a ground gutter.